In the field of implantable medical devices, implantable cardioverter/defibrillators (ICD), implantable pulse generators (IPG) and pacemaker/cardioverter/defibrillators (PCD) provide sensing of arrhythmias and programmable staged therapies including pacing regimens and cardioversion energy and defibrillation energy shock regimens in order to terminate a sensed arrhythmia with the most energy efficient and minimally traumatic therapies. In such implantable medical devices, the atrial and ventricular pacing pulse generators, sense amplifiers and associated timing operations are incorporated into a system having atrial and ventricular pace/sense medical electrical leads.
A wide variety of such pace/sense and defibrillation leads have been proposed for positioning endocardially within a heart chamber or associated blood vessel or epicardially about the heart chambers or more remotely in subcutaneous locations. Typically, the leads bear pace/sense/defibrillation electrodes with associated lead conductors and connector elements all of which are either incorporated into a single pacing lead body or into a combined pacing and defibrillation lead body.
In such implantable medical device systems, the integrity of the medical electrical leads is of great importance. Generally, the leads are constructed of small diameter, highly flexible, lead bodies made to withstand the environmental effects of body fluids. In addition, the leads must be able to function in the presence of dynamic body environments that apply chemical and physical stress and strain to the lead body and the connections made to electrodes or sensor terminals. Some of these stresses may occur during the implantation process. Months or years later, porosity that developed from those stresses may be magnified by exposure to body fluids. These, in turn, may result in conductor or insulation related conditions that may be manifested in an intermittent or sudden Loss of Capture (LOC), out-of-range impedance and/or Loss of Sensing (LOS).
Lead insulation breaches, interior lead conductor wire fracture or fractures with other lead parts have been known to occur. In the U.S. patent application Ser. No. 13/156,660 assigned to the present assignee, the various issues affecting the lead conductive pathway, which is comprised of one or both the conductor and insulation, and resulting in partial or complete short or open circuits, for example, have been referred to, for simplicity, as “lead-related conditions.” The Ser. No. 13/156,660 application explains that the lead-related conditions may manifest as static and/or intermittent/dynamic conductive discontinuities; a static conductive discontinuity may represent a conductive fracture resulting in conductor elements, such as filars or strands, being disconnected for an indefinite duration or until an intervention is performed while dynamic conductive discontinuity may represent a conductive fracture that results in transient or intermittent disconnections of the conductor elements for short durations in time. These lead-related conditions may lead to inappropriate implantable medical device responses if not mitigated or inhibited. For example, a transient that crosses the implantable medical device sense circuit thresholds may be misinterpreted as a physiological event. The perceived “physiological” event may lead to inappropriate implantable medical device algorithmic conclusions that may lead to undesired device operation.
Conventional approaches for detecting lead-related conditions have been limited to electrical behaviors leading to adverse system events. For example, filters have been employed in the sense circuits to eliminate high frequency signal components prior to threshold recognitions in the sense circuits. These filters may be designed to pass some frequency ranges and attenuate other frequency ranges and are effective for the frequency ranges they are designed to attenuate or pass, but are not consistently effective with signals or distortions that vary from those specified ranges. Several solutions have employed periodic testing that includes measurements of parameters such as lead impedance to determine when the integrity of the medical electrical lead is compromised. Other approaches to address lead body defects have been to construct the lead with re-engineered materials that are more robust.
However, there have been inherent limitations including expected and varying implant environmental conditions that eventually result in the emergence of lead-related conditions on the lead body. Another challenge associated with existing solutions is that the periodic measurements may not always correlate with the intermittent nature of the conductor make-break contact. Additionally, the periodic measurements and measurements triggered by apparent physiological signal aberrations may not identify lead-related conditions expeditiously for effective containment and to prevent error propagation.
As such, even with the robust lead body construction, there remains a need to provide for fault tolerant architectures including reconfiguration of lead functionality for continued system functionality and graceful degradation to promote safety.